The fluids that are recovered from an earth formation during a drill stem test of the well accumulate in the pipe string that suspends the test tools. For safety reasons, it is necessary and desirable to remove the fluid recovery from the pipe string before withdrawing the tools from the well at the end of a test, so that oil will not be spilled at the rig floor as pipe joints are disconnected. Of course, any spilled oil can constitute a highly undesirable fire hazard.
Thus it is typical practice to include in a string of drill stem testing tools a device generally known as a reverse circulating valve. A reverse circulating valve is a tool that includes a normally closed valve element which can be opened to provide open communication between the well annulus and the pipe string at a point above the main test valve so that pressure applied to the well annulus can displace the fluid recovery upwardly to the surface where it can be piped safely to suitable containers.
When a drill stem test is being conducted in an offshore well from a floating vessel, it has become fairly standard practice to use annulus pressure changes to actuate the various valves and the like that are employed in the tool string. A reverse circulating valve that opens after a number of pressure change cycles is disclosed in U.S. Pat. Nos. 3,850,250, 3,930,540 and 4,058,165. This valve has a long closure sleeve that is pulled in incremental amounts toward the open position in response to reciprocation of a pressure responsive mandrel that is connected to the closure sleeve by a ratchet system. In addition to being somewhat complex and lengthy, this approach has the disadvantage of automatic opening after a certain number of annulus pressure changes have been made, whereas a particular well test may require more flexibility in the number of pressure changes that need to be applied in the course of a testing program. It is desirable to provide for more surface control over the precise point in time that the test will be terminated and the reversing valve opened so that the pipe can be purged of well fluids. Other pressure responsive reverse circulating valves are disclosed in U.S. Pat. Nos. 4,063,593 and 4,064,937. However, both of these valves are constructed in combination with a dual ball valve sampler apparatus, with the resultant structures being quite complex due to the multiple functions that are intended to be performed. Still another approach is described in U.S. Pat. Nos. 3,970,147 and 4,044,829 where the reversing valve is held closed by a selected number of shear pins intended to control the pressure setting. However, machining inaccuracies can cause the pins to be loaded differently so that a particular setting is not repeatable, and the atmospheric chamber used in this type of design can result in high seal friction which can disturb the expected pressure setting.
It is the general object of the present invention to provide a new and improved annulus pressure controlled reverse circulating valve that is simpler in construction and operation and thus more reliable in use than has heretofore been known in the art.
Another object of the present invention is to provide a new and improved annulus pressure controlled reverse circulating valve that can be opened at any time that it is desired to terminate the test and without regard to the number of pressure change cycles previously employed to operate associated test tools.
Still another object of the present invention is to provide a new and improved reverse circulating valve of type described that is repeatable in operation and will open reliably when certain pressure increases are applied to the well annulus.